Historically, non-governmental voice communications over telephone networks have rarely been secured with an encryption product. This is largely due to the high expense typically associated with such a product, and the administrative burden of managing encryption keys among the devices. Yet the value of the information conveyed over telephone networks is increasing steadily. Telephone security products would see widespread use if their costs were reduced to the point where the corporate, financial, legal, medical, and industrial communities could afford them, and if the administrative tasks associated with the set-up and control of these products was minimized.
Existing telephone security products typically connect between the telephone and the telephone network. This typically permitted their application only on public-switched telephone networks (PSTNs), however, since they frequently interfere with proprietary services offered over private branch exchange (PBX) based telephone networks. In addition, these products usually cannot be applied to networks where proprietary digital PBXs or Integrated Services Digital Network (ISDN) protocols are employed since these interfaces are not standardized.
Thus, there is a need in the art for a small, inexpensive encryption device that can be connected between the handset and base unit of any of a variety of ordinary telephones to provide secure, full-duplex telephone conversations that are immune from eavesdropping with no degradation in speech quality.